The present invention relates to a system and method of monitoring a fiber processing apparatus that preferably is a disk refiner or a filter screen that can also manage apparatus inventory.
In fibrous product processing, such as the process used to make paper, fibers, such as wood fibers and cloth fibers, are separated and mixed with water and, if desired, other ingredients to form a fibrous stock slurry. This slurry is passed through a filter or a screening apparatus, typically referred to as a filter screen, a pressure screen, or a screen cylinder, that filters the slurry to remove from the slurry large particles, such as rocks, stones, metal fragments and the like, unrefined or untreated fiber, improperly sized fiber, as well as other contaminants. After filtering the slurry at least somewhat, the slurry is introduced to a refiner, typically a disc refiner, that grinds or abrades the fibers so they become more frayed or fibrillated. These frayed fibers are beneficial because they interlock with each other during manufacturing of the fiber product to produce a stronger fiber product. For example, where paper is being manufactured, frayed fibers beneficially increase the tensile and tear strength of the paper.
An example of a disc refiner is shown and disclosed in U.S. Pat. No. 5,425,508. The refiner has at least one pair of opposed ridged ring-shaped metal refiner plates that can be formed of pie-shaped refiner plate segments. During operation, one of the refiner plates rotates relative to the other of the refiner plates while the slurry flows under relatively high pressure into a gap between the plates where the plates grind or abrade the fibers.
As one would expect, the refiner plates, or segments of the plates, wear over time which can dramatically decrease the quality of the refining action, i.e. refiner performance, such that the fibers are less frayed than desired. While various parameters of refiner operation are usually monitored, it is believed not heretofore known to collectively monitor and analyze at least some of these parameters while a refiner is operating to attempt to detect or predict when the performance or a refiner plate (or plates) has degraded to the point that that the refiner plate, or segments of the plate, should be replaced. This is because many things other than plate wear can cause the performance of a refiner to at least temporarily decrease making it extremely difficult to detect when plate wear is primarily responsible. Examples of some things that can cause refiner performance to temporarily drop include non-fibrous matter in the stock slurry, a change in stock consistency, knots, and a change in the type or size of fibers being processed.
As a result of the uncertainty of what is responsible for a decrease in refiner quality or performance, refiner plates are typically replaced according to a schedule that mandates replacement after a certain number of hours of operation whether or not replacement is really needed. For example, a typical thermomechanical pulp (TMP) mill may require replacement of the primary plates of a refiner after 2,200 hours of operation and the reject plates of the refiner after 650 hours of operation, regardless of how well the refiner is performing. Because of this, refiners may operate at a less than optimum quality or performance level with plates that needed to be replaced earlier than dictated by the replacement schedule. In other instances, refiner plates that don""t need replacing are unnecessarily replaced in accordance with the replacement schedule causing needless downtime and wasting money.
The same is true for filter screens. As is disclosed in U.S. Pat. Nos. 4,954,249; 5,718,826; and 5,626,235, although filter screens can have other configurations, filter screens are often made of perforated and generally cylindrical screen plates, usually referred to as cylinder screens, that are held together by a frame that typically includes retaining rings and tie rods. Typically, two or more such screen plates are disposed end-to-end in a housing, forming a generally cylindrical screen assembly, with the plates held together by the tie rods that extend axially alongside the plates and which pass through the retaining rings.
Each screen plate is formed from metal wire, i.e. wedgewire, or from machined metal sheets. Each screen plate is perforated by holes that typically are slots of a predetermined size that permits objects in the slurry of a size smaller than one of the slots and liquid to pass through the plate. The material retained, referred to as rejects, is drawn away from the surface of the screen plate usually by the head of a moving foil that is located adjacent the screen assembly. The rejects are directed from the filter screen out a discharge port for disposal.
To help ensure that only the slurry is made up of only refined fibers and liquid when it reaches a fiber product processing machine, such as a paper machine, the slurry often passes through several stages of filter screens. Each filter screen typically has correspondingly smaller and smaller holes or slots such that it is possible to limit the size of the fibers that actually arrive at the fiber product-processing machine.
Unfortunately, screen plates wear rather slowly during operation and then rapidly degrade in performance in a rather short time, which makes screen plate failure difficult to predict. To prevent screen plate wear from adversely impacting the fiber product manufacturing process, screen plates are also changed according to a schedule. While the flow rate of the slurry through a particular filter screen can be monitored to provide some sort of an estimate of filter screen efficiency or quality, it is believed heretofore not known to collectively monitor and analyze this and other filter screen operating parameters to attempt to detect or predict when the performance of a screen plate has degraded to the point that it needs to be replaced.
Finally, because fiber product manufacturing processes often operate around the clock seven days a week, an inventory of replacement refiner plates and screen plates are usually kept nearby. Unfortunately, keeping an inventory of these plates takes up valuable and costly space that could be devoted to other more efficient aspects of fiber product production.
Therefore, what is needed is a system and method of managing an inventory of one or both refiner plates and screen plates that minimizes the storage space required at or nearby the fiber product manufacturing plant. What is also needed is a system and method of monitoring refiner performance to detect and preferably indicate when one or more plates of a refiner should be replaced. What is further needed is a system and method of monitoring filter screen performance to detect and preferably indicate when one or more screen plates of a filter screen should be replaced. What is still further needed is a system and method of monitoring refiners and filter screens to detect when one or more plates need to be replaced.
A system, software program, and method of monitoring operation of a fiber processing apparatus that preferably is either or both a refiner and a filter screen. The system includes a computer that is linked to a plurality of sensors that sense data that pertains to the operation of at least one fiber processing apparatus. The computer is configured with a program that monitors operating data pertaining to the operation of a fiber processing apparatus to help determine, estimate or predict about when a plate of the apparatus should be changed.
The operating data over a period of time of apparatus operation is monitored for a change in the data that indicates a trend toward reduced apparatus performance. The change is analyzed to determine whether it is attributable to plate wear or other factors not related to plate wear. If it is determined that the change is due to plate wear, a recommendation to replace the plate is generated.
In determining whether the change is due to plate wear, the operating data can be analyzed to detect whether performance has fallen below a threshold that indicates the plate should be changed. In one preferred method of determining whether to change the plate, a set of operating data over time is analyzed by a regression technique to determine whether a result or characteristic of the regression technique compared against the threshold indicates the change in data is due to plate wear.
In one preferred regression technique, linear regression or piecewise linearization is used to obtain a slope, an operating slope, of the operating data. The operating slope is compared with a threshold slope to determine whether the operating slope is within a certain acceptable window of the threshold slope that indicates that apparatus performance has not degraded sufficiently so as to warrant a recommendation to replace the plate. If the operating slope is outside the acceptable window, the recommendation to replace the plate is generated. In one preferred implementation, a plate change recommendation is generated if the slope is negative. In another preferred implementation, the plate change recommendation is generated if the slope is not within about 10% or 20% of the threshold slope.
The threshold slope is a slope of operating data taken at a time prior to at least some of the data upon which the operating slope is based. In one preferred implementation, the threshold slope is determined from a baseline obtained about when or shortly after the plate was first installed. In another preferred implementation, the threshold slope can be a prior operating slope or can be the slope from a set of data taken shortly before determining the operating slope. The threshold slope is based on data sufficient to provide a baseline from which change can be detected. If desired, the threshold slope can simply be a predetermined value that can be user defined.
To avoid transient fluctuations in data and apparatus performance from falsely triggering a plate change recommendation, data is taken over a large enough sampling period so as to filter out the fluctuations. For example, because the decline in performance of a refiner plate usually happens over a period of about one hundred hours, refiner-related data taken for a time of at least about the most recent fifty hours of refiner operation and no greater than about the most recent two hundred hours of refiner operation is used to determine the operating slope. In another example, because the decline in performance of a filter screen plate happens much more rapidly, typically within about an eight hour period, filter screen-related data is taken for a period of time of at least about the most recent four hours of filter screen operation and no greater than about the most recent twenty-four hours of filter screen operation is used to determine the operating slope.
In a preferred method of managing an inventory of fiber processing apparatus plates, the inventory is updated when one or more plates are added to the inventory or if one or more plates are removed from the inventory. Plates added to the inventory, such as when a shipment of plates are received, can be provided from a portable device that inputs or scans plate identification information of a tag of the plate being inventoried. The portable device is linked to the computer and the plate identification information is downloaded to the computer.
Plates removed from the inventory typically are removed when they are installed on a fiber processing apparatus. When a plate is installed on an apparatus, a record for that apparatus is updated to reflect the installed plate and to reflect that a different plate was removed from the apparatus. Each apparatus being monitored by the computer preferably has such a record. The plate removed goes to another record that keeps track of removed plates.
The inventory is monitored to determine whether the number of plates in the inventory has fallen below a desired threshold or below a desired threshold for a particular fiber processing apparatus. If so, replacement plates are automatically ordered preferably by a link to a remote computer that provides the order to a supplier of plates. Preferably, the link is a telecommunications link that permits the order to be placed by e-mail or by FTP connection with the supplier computer.
When an order is placed, confirmation of the order from the supplier computer preferably is received while the link with the supplier computer is established. If desired, the order confirmation can be displayed or printed.
It is an object of the present invention to more accurately detect when plate wear will or is about to so adversely affect performance of the fiber processing apparatus that it should be changed.
It is an advantage of the present invention that more accurate detection of plate wear enables plate use to be extended reducing plate replacement costs.
It is an object of the present invention to detect plate wear at an early enough stage before it significantly impacts the quality of the fiber-based product being produced.
It is an advantage of the present invention that it optimizes fiber processing by minimizing the impact of plate wear.
It is another object of the invention to filter out transient changes in performance unrelated to plate wear to maximize the useful life of the plate.
It is another advantage of the present invention that transient changes in performance are filtered to prevent them from triggering a plate change.
It is another object of the present invention to conveniently monitor operation and performance of more than one fiber processing apparatus that can be located in more than one place using a minimum of labor thereby saving money, time and labor.
Other objects, features, and advantages of the present invention include: a monitoring system that can advantageously interface with an existing fiber processing apparatus data acquisition system such as a paper mill""s distributed control system (DCS), a monitoring system that is capable of both monitoring apparatus performance while also maintaining and managing inventory of plates for the apparatus; that reduces fiber processing apparatus downtime; that maximizes fiber processing quality; that is flexible in that it can have thresholds that trigger a plate change recommendation that can be user defined, can be different for different types of refiners and filter screens, and can be adjusted for changes in a refiner or filter screen; and is a system and software program that is simple, flexible, reliable, and robust, and which is of economical manufacture and is easy to assemble, install, and use.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating at least one preferred embodiment of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.